Impulse reception



Dec. 3, 1940. P. KOTOWSKI arm. 2,223,995

IMPULSE RECEPTION Filed April 20, 1938 zlvvs/v'roms Paul Koi'owslii, Jigmunvl Jonnenfeld 3- Gottfr'ed Vogt I attorney Patented Dec. ,3, 1940 IMPULSE RECEPTION tion of Germany ,Application April 20, 1938, Serial No. 203,104

' In Germany April 22, 1937 1 Claim. (01. 250-20) I In the reception oflimpulses itooften happens that in addition to feeble ground wave impulses,

one ,or more powerful ionosphere impulses are impressed on the receiver. The receiver apparatus which is very responsive and sensitive to ground-wave impulses is overloaded because of the fact that the sky-wave impulses or echoes are occasionally .as much as 100 times stronger.

Such overloading causes :in the last high-frequency stages and also in the audio frequency stages the production of grid currents, and these cause the coupling condensers, especially those in the audio frequency stages, to become charged.

' The apparatus will be blocked for a time and will become ready for operation only after an interval of timegqverned bythecharging and discharging time constants of the R--'C elements. Where automatic volume. controlled receiver apparatus is concerned, there occursin addition 20. an overall retrogressive regulation of the responsiveness. Identical disturbing actions arise upon the production of strong atmospherics. Now, the method here disclosed according to the invention is designed to suppress both the said atmospheric 25* disturbances as well as powerful ionosphere echoes. In order to rapidly reduce the receiver sensitivity upon the reception of overloads, the blockingtime constants of the capacitors and resistors in thegrid circuits of the radio fre- 3 quency, intermediate frequency and audio frequency stages accordingtothis invention are to be made roughly equal to the impulse length.

In order that undue voltage peaks may be entirely prevented from reaching the audio fre- 35 quency part, a resistance or the approximate size of the alternating current resistance of the gridfilament path is included in the grid lead of the last radio, intermediate and audio frequency tubes of each stage, according to afurther object of 40 this invention.- The said resistance is intended to prevent a further growth of the grid alternating potentials upon incipient flow of grid current j tus has its maximum or optimum responsiveness o'r' sensitivity in the presence of new strengths of the ground-wave impulse of, say,'up to 50 microvolts per meter. After this point vhas been reached, a regulator action starts which may 7 55 even have a drooping characteristic. The receiver then hasits maximum sensitivity in the pres-- 'ence of potentials which surpass its own inherent noise by a factor of, say, 1 to 20. This invention will be better understood from the following description when considered in connection with the 5 accompanying drawings, in which Figure 1 is a schematic diagram of an embodiment of thisinvention, and Figure 2 is a curve illustrating the operation of this invention.

Referring now to Fig. 1, a portion of a radio 10 receiver is illustrated to show the application of an automatic volume control circuit. Reduction of sensitivity is effected in the usual way by means of a diode rectifier coupled to the intermediate frequency amplifier. Therectified voltage isapl5 plied to the control grids of the radio frequency pentodes. Unlike the usual control systems, however, the charging 'time constant of the volume control network is of the same order of magnitude as the impulse, say, 1 microsecond. The discharging time constant for restoring the normal sensitivity is so chosen that thereceiver sensitivity is normal upon arrival of the following ground impulse or direct impulse. Reference is made in this connection to Figure 2 where the amplitudes of the incoming ground impulse a and consecutive echoes b1, b2, and be are plotted against time t. This time constant is governed by the elements Rv, R, and C, Fig. 1. The dotted line indicates the limiting effect of the volume control system.

, Under practical conditions, low time constants are obtained by reducing the resistances and the condensers of the R C means, though the fluctuation of the internal resistance of the diode must here be duly taken into consideration. Small time constants, moreover, oifer the advan tage that low-pitched modulation frequencies will not be transmitted because of the smallness of the values of R and C. In fact, they cause down-, ward regulation of the low modulation frequencies. In other words, if an impulse transmitter radiates an appreciable hum this sound will appear only to a very small degree in the incoming signals. v

. 5 Another chance of using the method here dis- 4 closed is that in a heterodyne receiver apparatus A receiver for the-reception of short signals;

pulses separated by discrete intervals, said receiver having means for rectifying said pulses to produce a charging pulse, a capacitor, means for applying said charging pulse to said capacitor to charge said capacitor within a time comparable to the duration of said signal pulse, means for discharging said capacitor within a time comparable to one-half the length of said discrete intervals, and means for reducing the sensitivity of said receiver in accordance with the amplitude of the voltage across said capacitor.

PAUL KOTOWSKI.

SIGMU'ND H. SONNENFELD. GOTTFRIEHD VOGT. 

